In a turbo charger in which a turbine is rotated by the exhaust gas from an engine and air is supplied to the engine after being compressed by a compressor arranged on the same axis with the turbine, an electronically controlled actuator drives opening and closing of nozzle vanes mounted on a turbine nozzle to adjust the turbo-charging pressure of the compressor.
FIG. 7 is a cross-sectional view showing the configuration of a conventional electronically controlled actuator 100 arranged around a turbo charger. In the turbo charger, an intake-side compressor housing 2 and an exhaust-side turbine housing 3 are arranged to face each other, while a compressor and turbine housed therein are arranged on the same axis. This axis is arranged within a bearing housing 4 which links the compressor housing 2 and the turbine housing 3. In the conventional electronically controlled actuator 100, a motor 101 is arranged at a position close to the turbine housing 3, and a motor shaft 102, a pinion gear 103 coupled with the motor shaft 102 and a plurality of gears 104, 105 are arranged on the side of the compressor housing 2 to thus transmit the rotation driving force of the motor 101 to the shaft 106. Then, the end portion of the shaft 106 is led out toward the turbine housing 3 and connected to nozzle vanes (not shown) within the turbine housing 3. This configuration has a drawback that the temperature of the motor is increased by receiving the radiation heat from the turbine housing 3 heated by the exhaust gas of the engine, which shorten remarkably the lifetime of the motor and hence the lifetime of the actuator. For this reason, it is necessary that a part of the motor 101 facing the turbine housing 3 be covered with a heat shield 107 to protect the motor 101 against the radiation heat.
In addition, in order to protect the electronically controlled actuator against the heat, for example, in Patent Document 1, the part of the electronically controlled actuator exposed from the engine is arranged at a position displaced in a direction of vehicle width from a heat generator arranged around the engine so as to prevent the actuator from being exposed to the heat.
Further, in an electronically controlled actuator according to Patent Document 2, for example, a unit cover for housing a motor control board, a motor casing for housing a motor, and an actuator cover for housing a reduction gear mechanism composed of a pinion gear and a plurality of reduction gears are formed separately, while the unit cover and the actuator are made of an aluminum alloy for protection against heat.